This invention relates to a thrust bearing arrangement for the propeller shaft of marine outboard drives and more particularly to an improved thrust bearing arrangement.
In marine outboard drives, be they either the lower unit of an outboard motor or the lower unit of the outboard portion of an inboard/outboard drive, it is the normal practice to embody a selectively operable forward, neutral and reverse transmission. As a result, the propeller shaft must be capable of transmitting both forward and reverse driving thrusts to the lower unit. Due to the relatively compact nature of marine outboard drives, this has presented certain problems in providing adequate thrust bearing arrangements and yet thrust bearing arrangements that will provide long life and good serviceability.
In one type of thrust bearing arrangement for such marine outboard drives, it has been the practice to employ a single thrust flange on the propeller shaft and a pair of oppositely disposed thrust bearings that cooperate with this flange so as to take both forward and reverse driving thrusts. With the prior art constructions of the type described, the thrust bearings have been held between a pair of bearing housings which are, in turn, held in engagement with the thrust bearing and flange by supporting bolts or bolt and nut assemblies. Although this arrangement provides a relatively compact configuration, the reverse loadings on the propeller shaft tend to cause the bolt and nut assemblies to work loose and the thrust bearings will become loose and worn.
It is, therefore, a principal object of this invention to provide an improved thrust bearing arrangement for a marine outboard drive.
It is a further object of this invention to provide an improved thrust bearing arrangement for marine outboard drives wherein the thrusts are transmitted by the forward and reverse thrust bearings directly to the lower unit housing and independently of each other. The term "independently of each other" is used herein to mean that the thrust from the individual thrust bearings is transmitted to the lower unit housing without the thrusts from both bearings having to pass through a common element.
Although there are some advantages in connection with the use of only a single thrust flange on the propeller shaft, such a configuration locates both the forward and reverse driving thrusts in the same area of the lower unit housing. Certain advantages may be obtained if the respective driving thrusts are confined to spaced apart areas of the lower unit housing.
It is, therefore, a still further object of this invention to provide a thrust bearing arrangement for a marine outboard drive wherein forward and reverse thrusts are transmitted to the lower unit housing at axially spaced apart locations.
In normal outboard motors or outboard drives, the forwardly disposed gear of the forward, neutral, reverse transmission is the forward driving gear and the forward driving thrusts may be transmitted directly from it to the lower unit housing. However, where there are twin outboard drives, it is the practice to employ drive shafts that drive in the same directions. As a result, the added outboard drive is operated so that its rearwardly disposed gear is the forward drive gear and a different thrust taking arrangement must be provided. One way in which this may be done is by providing a splined connection between the transmission output shaft and the propeller shaft so that the thrusts may be taken directly by the propeller shaft rather than by the gears of the transmission. This also has the advantage of reducing the thrusts which are exerted from this gear to the driving bevel gear of the transmission when the rear gear is the forward drive gear. This problem does not exist when the front gear is the forward drive gear.
It is, therefore, yet another object of this invention to provide an improved thrust taking arrangement for the added outboard drive of a twin outboard arrangement.